Semiconductor device and manufacturing method thereof

ABSTRACT

An object is to provide a semiconductor device with improved reliability in which a defect stemming from an end portion of a semiconductor layer provided in an island shape is prevented, and a manufacturing method thereof. Over a substrate having an insulating surface, an island-shaped semiconductor layer is formed, a first alteration treatment is performed, a first insulating film is formed on a surface of the island-shaped semiconductor layer, the first insulating film is removed, a second alteration treatment is performed on the island-shaped semiconductor from which the first insulating film is removed, a second insulating film is formed on a surface of the island-shaped semiconductor layer, and a conductive layer is formed over the second insulating film. An upper end portion of the island-shaped semiconductor layer has curvature by the first alteration treatment and the second alteration treatment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and amanufacturing method of a semiconductor device. Note that in thisspecification, a semiconductor device refers to devices in general thatfunction by utilizing a semiconductor characteristic.

2. Description of the Related Art

In recent years, manufacturing of semiconductor devices that utilizethin film transistors as switching elements, in which the thin filmtransistors (hereinafter also referred to as a “TFT”) are formed oversubstrates having insulating surfaces, such as glass, has been activelypursued. In the thin film transistor, an island-shaped semiconductorlayer is formed over a substrate that has an insulating surface, and aportion of the island-shaped semiconductor layer is used as achannel-forming region of the transistor.

Patent Document 1: Japanese Published Patent Application No. H8-335702

Patent Document 1: Japanese Published Patent Application No. H3-22567

SUMMARY OF THE INVENTION

However, with a thin film transistor that has an island-shapedsemiconductor layer, there is concern of various defects occurring at anend portion of the semiconductor layer. For example, when thesemiconductor layer is formed in an island shape, a step is formed at anend portion of the semiconductor layer, and coverage by a gateinsulating film tends to be poor at the end portion of the semiconductorlayer. For example, at the end portion of the island-shapedsemiconductor layer, there is a case where the gate insulating filmbecomes thin locally. In a case where the end portion of theisland-shaped semiconductor layer cannot be covered sufficiently by thegate insulating film, there is concern of a short circuit occurringbetween a conductive layer that serves as a gate electrode and thesemiconductor layer, or a leak current occurring. Particularly in recentyears, reduction in film thickness of gate insulating films is desiredin order to reduce power consumption of thin film transistors as well asimprove operation speed thereof, and when a gate insulating film isprovided to be thin, a defect in coverage of an end portion of asemiconductor layer becomes an even more pronounced problem.

Further, at an end portion of an island-shaped semiconductor layer,particularly a region in which a conductive layer that serves as a gateelectrode and the semiconductor layer overlap, an electric fieldconcentrates easily at the end portion (corner portion). When anelectric field concentrates, there is a problem of a leak currentoccurring due to dielectric breakdown or the like of the gate insulatingfilm, formed between the conductive layer that serves as a gateelectrode and the semiconductor layer. In addition, the defect incoverage by the gate insulating film also leads to electrostaticdischarge (ESD) or the like of an element or the gate insulating film,and causes yield reduction in manufacturing a semiconductor device.

When a problem such as the above that stems from an end portion of asemiconductor layer occurs, an operational characteristic of a thin filmtransistor becomes degraded and reliability also decreases. Further, inmanufacturing a semiconductor device, yield also decreases. In view ofthese problems, an object of the present invention is to provide asemiconductor device with a novel structure with improved reliability,and a manufacturing method thereof.

One aspect of a manufacturing method of the present invention is that anisland-shaped semiconductor layer is formed over a substrate having aninsulating surface, a first insulating film is formed on a surface ofthe island-shaped semiconductor layer by performing a first alterationtreatment, the first insulating film is removed, a second insulatingfilm is formed on a surface of the island-shaped semiconductor layer byperforming a second alteration treatment on the island-shapedsemiconductor layer from which the first insulating film is removed, anda conductive layer is formed over the second insulating film. Further,an upper end portion of the island-shaped semiconductor layer hascurvature by the first alteration treatment and the second alterationtreatment.

Another aspect of a manufacturing method of the present invention isthat an island-shaped semiconductor layer is formed over a substratehaving an insulating surface, a first insulating film is formed on asurface of the island-shaped semiconductor layer by performing a firstalteration treatment, the first insulating film is removed, a secondinsulating film is formed on a surface of the island-shapedsemiconductor layer by performing a second alteration treatment on theisland-shaped semiconductor layer from which the first insulating filmis removed, and a conductive layer is formed over the second insulatingfilm. Further, an upper end portion and a lower end portion of theisland-shaped semiconductor layer have curvatures by the firstalteration treatment and the second alteration treatment.

Still another aspect of a manufacturing method of the present inventionis that an island-shaped semiconductor layer is formed over a substratehaving an insulating surface, a first insulating film is formed on asurface of the island-shaped semiconductor layer by performing a firstalteration treatment, the first insulating film is removed, a secondinsulating film is formed on a surface of the island-shapedsemiconductor layer by performing a second alteration treatment on theisland-shaped semiconductor layer from which the first insulating filmis removed, the second insulating film is removed, a third insulatingfilm is formed on a surface of the island-shaped semiconductor layer byperforming a third alteration treatment on the island-shapedsemiconductor layer from which the second insulating film is removed, aconductive layer is formed over the third insulating film. Further, anupper end portion and a lower end portion of the island-shapedsemiconductor layer by the first alteration treatment, the secondalteration treatment, and the third alteration treatment.

Note that in this specification, an alteration treatment refers to anoxidation treatment, a nitridation treatment, an oxynitridationtreatment, a surface modification treatment, or the like performed on asubstrate, a semiconductor layer, an insulating film, or a conductivelayer.

One aspect of a manufacturing method of the present invention is that afirst alteration treatment, a second alteration treatment, and a thirdalteration treatment are plasma treatments. Note that in thisspecification, a plasma treatment includes in its category an oxidationtreatment, a nitridation treatment, an oxynitridation treatment, and asurface modification treatment each using plasma, which is performed ona substrate, a semiconductor layer, an insulating film, or a conductivefilm.

One aspect of a manufacturing method of the present invention is that anisland-shaped semiconductor layer has a film thickness of 10 nm to 30 nminclusive.

Another aspect of a manufacturing method of the present invention isthat an insulating film has a film thickness of 1 nm to 10 nm inclusive.

Further, one aspect of a structure of the present invention includes asubstrate having an insulating surface, a semiconductor layer providedover the substrate, an insulating film formed so as to cover thesemiconductor layer, and a conductive layer provided over thesemiconductor layer with the insulating film interposed therebetween.Further, an upper end portion of a cross-section of the semiconductorlayer has a rounded shape.

Another aspect of a structure of the present invention includes asubstrate having an insulating surface, a semiconductor layer providedover the substrate, an insulating film formed so as to cover thesemiconductor layer, and a conductive layer provided over thesemiconductor layer with the insulating film interposed therebetween.Further, an upper end portion and a lower end portion of a cross-sectionof the semiconductor layer have rounded shapes.

Note that in this specification, an end portion refers to a rim portion(edge portion) of a semiconductor layer formed in an island shape.

One aspect of a structure of the present invention is that asemiconductor layer has a film thickness of 10 nm to 30 nm inclusive.

Another aspect of a structure of the present invention is that aninsulating film has a film thickness of 1 nm to 10 nm inclusive.

Yet another aspect of a structure of the present invention is that whena film thickness of a semiconductor layer is t (t>0) and a curvatureradius of an end portion of a cross-section of the semiconductor layeris r (r>0), a relationship of t and r satisfies a conditional formula(t/2)≦r≦2t.

Still another aspect of a structure of the present invention is thatwhen a film thickness of a semiconductor layer is t (t>0) and acurvature radius of an end portion of a cross-section of thesemiconductor layer is r (r>0), a relationship of t and r satisfies aconditional formula (t/4)≦r≦t.

One aspect of a structure of the present invention is that an insulatingfilm includes a material of a semiconductor layer.

By applying the present invention, a semiconductor layer can be reducedin thickness. Further, by an end portion of the semiconductor layerhaving curvature, a defect that stems from the end portion of thesemiconductor layer can be reduced. Therefore, an effect that acharacteristic of the end portion of the semiconductor layer has on thesemiconductor device can be reduced, and a semiconductor device withimproved reliability can be provided. In addition, in manufacturing asemiconductor device, yield can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C show an example of a main structure of a semiconductordevice according to the present invention;

FIGS. 2A to 2E show an example of a manufacturing method of asemiconductor device according to the present invention;

FIGS. 3A to 3C show an example of a manufacturing method of asemiconductor device according to the present invention;

FIGS. 4A and 4B show an apparatus capable of oxidation by plasmatreatment and nitridation by plasma treatment;

FIGS. 5A to 5E show an example of a manufacturing method of asemiconductor device according to the present invention;

FIGS. 6A to 6C show an example of a manufacturing method of asemiconductor device according to the present invention;

FIGS. 7A to 7F show an example of a manufacturing method of asemiconductor device according to the present invention;

FIGS. 8A to 8D show an example of a manufacturing method of asemiconductor device according to the present invention;

FIG. 9 is a block diagram showing an example of a semiconductor deviceaccording to the present invention;

FIG. 10 is perspective view showing an example of a semiconductor deviceaccording to the present invention;

FIG. 11A is an example of a top structure of a semiconductor device andFIGS. 11B and 11C show schematic cross-sectional views of FIG. 11Aaccording to the present invention;

FIGS. 12A to 12D show antennas that can be applied to a semiconductordevice according to the present invention;

FIGS. 13A to 13C are a block diagram showing an example of asemiconductor device according to the present invention and diagramsshowing usage examples thereof; and

FIGS. 14A to 14H each shows a usage example of a semiconductor deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Mode

Embodiment modes of the present invention will be explained below withreference to the drawings. However, it is to be easily understood bythose skilled in the art that the present invention is not limited tothe description below and the modes and details of the present inventioncan be changed in various ways without departing from the spirit andscope of the present invention. Therefore, the present invention shouldnot be interpreted as being limited to the description of the embodimentmodes below. Note that in the following description of the presentinvention, reference numerals denoting identical portions may be used incommon in different drawings.

Embodiment Mode 1

FIGS. 1A to 1C are a top view and cross-sectional views for describing amain structure of a semiconductor device according to the presentinvention. FIGS. 1A to 1C shows a structure of a thin film transistor inparticular, and FIG. 1A shows the top view, FIG. 1B shows across-sectional view across a dashed line O-P in FIG. 1A, and FIG. 1Cshows a cross-sectional view across a dashed line Q-R in FIG. 1A. Notethat in FIG. 1A, a thin film or the like is partially omitted.

A thin film transistor 113 shown in FIGS. 1A to 1C includes asemiconductor layer 103 provided in an island shape over a substrate 101with an insulating film 102 a and an insulating film 102 b interposedtherebetween; an insulating film 104 and an insulating film 105 formedover the semiconductor layer 103, a conductive layer 106 that serves asa gate electrode that is provided over the insulating film 104 and theinsulating film 105; and conductive layers 110 a and 110 b each servingas a source electrode or a drain electrode that are provided through aninsulating film 107 and an insulating film 108 over the conductive layer106.

As shown in FIGS. 1B and 1C, upper end portions of a cross-section ofthe semiconductor layer 103 are formed to have curvature. Further, upperend portions of the insulating films 104 and 105 provided over thesemiconductor layer 103 are also formed to have curvature. By providingcurvature in the cross-sectional upper end portions of the semiconductorlayer 103, coverage by the insulating films 104 and 105 at the endportions of the semiconductor layer 103 can be good. Consequently, adefect stemming from a defect in coverage by the insulating films 104and 105 at the end portions of the semiconductor layer 103, for example,a short circuit of the semiconductor layer and the gate insulating film,occurrence of a leak current, electrostatic breakdown, or the like canbe prevented.

For the substrate 101, a glass substrate, a quartz substrate, a sapphiresubstrate, a ceramic substrate, a metal substrate with an insulatingfilm formed on a surface, or the like can be used.

The semiconductor layer 103 is formed over the substrate 101. Theinsulating film 102 a and the insulating film 102 b serving as a baseinsulating film may be provided between the substrate 101 and thesemiconductor layer 103. The base insulating film prevents contaminationof the semiconductor layer 103 that is caused by diffusion of animpurity such as an alkali metal from the substrate 101, and may beprovided as a blocking layer as appropriate. Further, the baseinsulating film may be provided as a film that smoothes a surface of thesubstrate 101 when the surface has asperity.

The insulating films 102 a and 102 b are formed using silicon oxide,silicon nitride, silicon oxynitride, silicon nitride oxide, or the like.Further, in this embodiment mode, although the base insulating film hasa two-layer stacked-layer structure of the insulating films 102 a and102 b, a single-layer structure or a stacked-layer structure with threeor more layers may be employed. For example, as shown in this embodimentmode, in the case of a stacked-layer structure with two layers, asilicon nitride oxide layer can be formed as a first layer and a siliconoxynitride layer can be formed as a second layer. Further, a siliconnitride layer may be formed as the first layer and a silicon oxide layermay be formed as the second layer.

The semiconductor layer 103 is formed in an island shape. A variety ofsemiconductors can be used for the semiconductor layer 103, such as anamorphous semiconductor, a crystalline semiconductor, a polycrystallinesemiconductor, or a microcrystalline semiconductor. Specifically, asemiconductor material such as silicon, germanium, or silicon-germaniumcan be used to form the semiconductor layer 103. The semiconductor layer103 is formed to have a film thickness in the range of 10 nm to 150 nminclusive, preferably 10 nm to 100 nm inclusive, and more preferably 10nm to 30 nm inclusive.

By forming the semiconductor layer 103 to be a thin film of 50 nm orthinner, a TFT can be even more miniaturized. Further, even in a case ofincreasing an amount of the impurity element for doping thechannel-forming region in order to make a threshold voltage of the TFTsmall, since manufacturing of a fully-depleted TFT is made easier byforming the semiconductor layer 103 as a thin film, a TFT with a small Svalue and a low threshold voltage can be manufactured.

The semiconductor layer 103 includes a channel-forming region 111 andimpurity regions 112 a and 112 b each serving as a source region or adrain region. An impurity element imparting one conductivity type isadded to each of the impurity regions 112 a and 112 b. Further, animpurity element imparting one conductivity type for controlling athreshold voltage of a transistor may be added to the channel-formingregion 111. The channel-forming region 111 is formed in a region thatroughly matches a location of the conductive layer 106 with theinsulating film 104 and the insulating film 105 formed therebetween, andis also located between the impurity regions 112 a and 112 b.

In addition, a low-concentration impurity region that serves as alightly doped drain (LDD) region may be formed in the semiconductorlayer 103. The low-concentration impurity region can be formed betweenthe channel-forming region 111 and the impurity regions 112 a and 112 beach serving as a source region or a drain region. Note that thelow-concentration impurity region is to have a lower impurityconcentration compared to those of the impurity regions 112 a and 112 beach serving as a source region or a drain region.

The insulating film 104 is formed to be in contact with thesemiconductor layer 103, and the insulating film 105 is formed over theinsulating film 104. In addition, the conductive layer 106 is formedover the insulating film 104 and the insulating film 105. The insulatingfilm 104 and the insulating film 105 serve as a gate insulating film ofthe thin film transistor 113. That is, a gate insulating film accordingto the present invention can be formed as a single-layer structure or asa stacked-layer structure of two layers or more. Note that a borderbetween the plurality of insulating films does not have to be clear.

As described above, when the semiconductor layer 103 is formed in anisland shape, various defects stemming from the end portion of thesemiconductor layer 103 occurs easily. For example, at an end portion ofthe semiconductor layer 103 that overlaps with the gate electrode, andat an end portion of the channel-forming region 111 formed in thesemiconductor layer 103 where the semiconductor layer 103 overlaps withthe gate electrode (around borders between the channel-forming region111 and the impurity regions 112 a and 112 b each serving as a sourceregion or a drain region), the defects easily occur and are easilyeffected by electrostatic breakdown, or the like.

As causes of the defects, the following can be given. In a region wherean end portion of the channel-forming region 111 and the gate electrodeoverlap, a parasitic channel is easily formed through the gateinsulating film that is in contact with a side surface of the endportion of the channel-forming region 111 (end portion of thesemiconductor layer); a high voltage is applied to regions of the endportion of the channel-forming region 111 around the borders with theimpurity regions 112 a and 112 b each serving as a source region or adrain region compared to around the center of the channel-forming region111; there is an effect of etching or the like that is performed inprocessing the gate electrode (conductive layer) formed in a layerabove; and the gate insulating film is locally thin at the end portionsof the semiconductor layer 103.

Therefore, by the end portions of the semiconductor layer 103 havingcurvature and having good coverage by the insulating layers 104 and 105that serve as the gate insulating film, defects stemming from poorcoverage by the insulating film at the end portions of the semiconductorlayer 103, for example, a short circuit between the semiconductor layerand the gate electrode, occurrence of a leak current, electrostaticbreakdown, or the like can be prevented.

In this specification, an “end portion” of the semiconductor layerrefers to a rim portion (edge portion) of a semiconductor layer formedin an island shape.

When the thickness of the island-shaped semiconductor layer 103 is t(t>0) and the curvature radius at each of the end portions of theisland-shaped semiconductor layer 103 is r (r>0), the relationship of tand r satisfies a conditional equation (t/2)≦r≦2t. Further, when thecurvature radius of each of the end portions is r, a curvature centerlocation 120 exists on a substrate side.

Each of the insulating film 104 and the insulating film 105 can beformed using a material such as silicon oxide, silicon nitride, siliconoxynitride, silicon nitride oxide, aluminum nitride, silicon oxidecontaining fluorine (SiOF), silicon oxide containing carbon (SiOC),diamond-like carbon (DLC), or porous silica.

The conductive layer 106 that serves as a gate electrode is formed overthe semiconductor layer 103 with the insulating film 104 and theinsulating film 105 interposed therebetween. The conductive layer 106can be formed using a metal element such as tantalum, tungsten,titanium, molybdenum, chromium, aluminum, copper, or niobium, or analloy material or compound material containing the metal element. As thecompound material, a nitrogen compound, an oxygen compound, a carboncompound, a halogen compound, or the like can be used; specifically,tungsten nitride, titanium nitride, aluminum nitride, or the like can begiven. The conductive layer 106 is formed using one or a plurality ofthese materials to have a single-layer structure or a stacked-layerstructure. Further, the conductive layer 106 may be formed usingpolycrystalline silicon to which an impurity element imparting oneconductivity type such as phosphorus is added, or the like.

The insulating film 107 and the insulating film 108 that serve as aninterlayer insulating film are formed so as to cover the conductivelayer 106. In this embodiment mode, the interlayer insulating film isformed as a stacked-layer structure of the insulating film 107 and theinsulating film 108. Each of the insulating film 107 and the insulatingfilm 108 can be formed using a silicon nitride film, a silicon nitrideoxide film, a silicon oxynitride film, a silicon oxide film, or anotherinsulating film containing silicon. The interlayer insulating film maybe formed as a single-layer structure or a stacked-layer structureincluding three layers or more.

Further, contact holes (opening portions) 109 a and 109 b that reach thesemiconductor layer 103 are formed in the insulating films 104, 105,107, and 108. Also, the conductive layers 110 a and 110 b are formed soas to cover the contact holes 109 a and 109 b, respectively. Each of theconductive layers 110 a and 110 b serves as a source electrode or adrain electrode, and is electrically connected to a portion of thesource region or drain region. Each of the conductive layers 110 a and110 b is formed using a metal such as silver, gold, copper, nickel,platinum, lead, iridium, rhodium, tungsten, aluminum, tantalum,molybdenum, cadmium, zinc, iron, titanium, zirconium, or barium; Si orGe; or an alloy or a nitride thereof. In addition, a stacked-layerstructure thereof may be used.

A semiconductor device according to this embodiment mode can be evenmore miniaturized by forming a semiconductor layer to be a thin film of50 mm or thinner. Further, by an end portion of the semiconductor layerhaving curvature, a defect stemming from the end portion of thesemiconductor layer can be reduced Consequently, a semiconductor devicewith high reliability can be manufactured. In addition, semiconductordevices can be manufactured with good yield.

Next, an example of a manufacturing method of the semiconductor deviceshown in FIGS. 1A to 1C is described in specific with reference to FIGS.2A to 3C.

First, the insulating films 102 a and 102 b that serve as a baseinsulating film are formed over the substrate 101, and the island-shapedsemiconductor layer 103 is formed over the insulating films 102 a and102 b (see FIG. 2A). As the substrate 101, a glass substrate, a quartzsubstrate, a sapphire substrate, a ceramic substrate, a metal substratewith an insulating film formed on a surface, or the like can be used.

Each of the insulating films 102 a and 102 b is formed by a CVD method,a sputtering method, an atomic layer deposition (ALD) method, or thelike, using a material such as silicon oxide, silicon nitride, siliconoxynitride, or silicon nitride oxide. The insulating films 102 a and 102b serve as blocking layers that prevent contamination of thesemiconductor layer 103 that is caused by diffusion of an alkali metalor the like from the substrate 101. Further, the insulating films 102 aand 102 b serves as films that smooth a surface of the substrate 101when the surface has asperity. Note that the insulating films 102 a and102 b do not have to be formed if impurity diffusion from the substrate101 and asperity of a substrate surface are not a problem. Also,although the base insulating film has a stacked-layer structure of twolayers in this embodiment mode, it may have a single-layer structure ora stacked-layer structure of three or more layers.

For the semiconductor layer 103, an amorphous semiconductor manufacturedby a vapor growth method or a sputtering method using a semiconductormaterial gas typified by silane or germane (hereinafter also referred toas “amorphous silicon (AS)”); a polycrystalline semiconductor made bycrystallizing the amorphous semiconductor with light energy or heatenergy; or a semi-amorphous (also called “microcrystal,” and alsoreferred to as “SAS” below) semiconductor can be used. For example, theisland-shaped semiconductor layer 103 can be formed by crystallizing asemiconductor layer formed over an entire surface of the substrate 101by a vapor growth method or a sputtering method, and then etching thesemiconductor layer as selected.

As a material forming the semiconductor layer 103, it is preferable touse a material mainly containing silicon. Specifically, silicon,silicon-germanium, or the like can be used. Also, germanium may be used.

As a crystallization method of the semiconductor layer, a lasercrystallization method, a heat crystallization method using rapidthermal annealing (RTA) or an annealing furnace; a crystallizationmethod using a metal element that promotes crystallization; a methodcombining these methods; or the like can be used.

In the case of using a laser crystallization method, a laser beamemitted from a continuous wave laser (hereinafter also referred to as a“CW laser”) or a pulsed wave laser (hereinafter also referred to as a“pulsed laser”) can be used. As a laser which can be used here, a gaslaser such as an Ar laser, a Kr laser, an excimer laser, a copper vaporlaser, or a gold vapor laser, or a solid-state laser such as a laserwhose medium is single-crystal YAG, YVO₄, or forsterite (Mg₂SiO₄),YAlO₃, or GdVO₄, to which one or more of Nd, Yb, Cr, Ti, Ho, Fr, Tm, andTa has been added as a dopant, or polycrystalline (ceramic) YAG, Y₂O₃,YVO₄, YAlO₃, or GdVO₄, to which one or more of Nd, Yb, Cr, Ti, Ho, Er,Tm, and Ta has been added as a dopant; a glass laser; an alexandritelaser; a ruby laser; or a Ti:sapphire laser; or the like can be given.In the case of using the solid-state laser, any of the fundamental waveto fourth harmonic thereof can be selected as appropriate forirradiation. For example, the second harmonic (532 nm) or the thirdharmonic (355 nm) of an Nd:YVO₄ laser (the fundamental wave: 1064 nm)can be used. When an Nd:YVO₄ laser is used as a CW laser, a laser powerdensity of about 0.01 to 100 MW/cm² preferably, 0.1 to 10 MW/cm²) isrequired, and irradiation is conducted with a scanning rate of about 10to 2000 cm/sec. Note that the second harmonic (532 nm) is preferablyused here; this is because the second harmonic is superior in energyefficiency to the harmonics higher than this.

When laser crystallization is performed using a CW laser, asemiconductor layer continuously receives energy; therefore, once thesemiconductor layer is melted, the melted state can be continuous.Therefore, it is possible to move a solid-liquid interface of thesemiconductor layer by scanning with a CW laser beam and to form acrystal grain which is elongated in one direction along this scanningdirection. A solid-state laser is preferably used because its output isso stable that a stable process can be expected compared to a gas laseror the like. By using not only a CW laser but also a pulsed laser with arepetition rate of greater than or equal to 10 MHz, the similar effectcan be obtained. In the case of a pulsed laser with a high repetitionrate, when the pulse interval of the laser is shorter than the periodafter the semiconductor layer is melted and before the meltedsemiconductor layer is solidified, the semiconductor layer can bemaintained in a melted state at all times. Also, by movement of thesolid-liquid interface, a semiconductor layer including a crystal grainwhich is elongated in one direction can be formed. Moreover, oscillationof a laser beam with TEM₀₀ (single transverse mode) is preferablebecause the energy homogeneity of a linear beam spot on an irradiationsurface can be improved.

The semiconductor layer 103 can be formed into an island-shape by thesteps of covering the semiconductor layer formed over the entire surfaceof the substrate with a mask made of a resist as selected and etchingthe semiconductor layer not covered with the mask made of a resist. Thesemiconductor layer can be etched by a dry etching method or a wetetching method. In the case of dry etching, an etching gas with highetching selectivity respect to the base insulating film is used. Thatis, an etching gas with a low etching rate with respect to theinsulating films 102 a and 102 b and a high etching rate with respect tothe semiconductor layer 103 may be used. As an etching gas, for example,a chlorine-based gas such as C₂, BCl₃, or SiCl₄, a fluorine-based gassuch as CF₄, NF₃, or SF₆, or a bromine-based gas such as HBr gas can beused. Further, an inert gas such as He, Ar, Ne, Kr, or Xe may be addedas appropriate. Furthermore, an O₂ gas may be added to a fluorine-basedgas as appropriate. After the semiconductor layer is processed into adesired shape, the mask is removed.

The island-shaped semiconductor layer 103 may be formed such that across section of the end portion has a tapered form that is nearly at aright angle, or a tapered form with a gentle incline. For example, theend portion may be tapered such that a taper angle is greater than orequal to 45° and less than 95°, preferably, greater than or equal to 60°and less than 95°, or may be tapered with a gentle incline such that ataper angle is less than 45°. The shape of the end portion of thesemiconductor layer 103 can be selected as appropriate by changing theetching condition or the like.

Note that for the semiconductor layer 103, an SOI substrate of which asingle-crystal semiconductor layer is provided over an insulatingsurface may be used instead of performing a thin film process that usesvarious crystallization methods. In this case, the semiconductor layer103 can be formed using the single crystal semiconductor layer providedover the insulating surface.

Next, as shown in FIG. 2B, an insulating film 115 is formed on a surfaceof the semiconductor layer 103 by performing an alteration treatment onthe semiconductor layer 103. Here, the alteration treatment refers to anoxidation treatment, a nitridation treatment, an oxynitridationtreatment, a surface modification treatment, or the like performed on asubstrate, a semiconductor layer, an insulating film, and a conductivelayer. A desired treatment may be performed in a region of thesemiconductor layer 103 where the insulating film 115 is to be formed.Specifically, a thermal oxidation treatment, a treatment with a solutionthat has strong oxidative power such as ozone water, a plasma treatment,or the like is performed on a surface of the semiconductor layer 103, sothat an oxide of the semiconductor layer 103 is formed on thesemiconductor layer 103. This also applies to cases of forming anitride, an oxynitride, and a nitride oxide of the above semiconductorlayer 103. By forming the insulating film 115, the semiconductor layer103 can be reduced in thickness. Note that by performing a plasmatreatment on the semiconductor layer 103, controlling a thickness of theinsulating film 115 becomes easy.

Next, as shown in FIG. 2C, the insulating film 115 is removed byetching. A method of removing the insulating film 115 may be dry etchingor wet etching. For example, in a case of performing dry etching,chlorine-based gas such as Cl₂, BCl₃, or SiCl₄, a fluorine-based gassuch as CF₄, NF₃, or SF₆, fluorocarbon gas such as CHF₃, C₅F₈, or C₄F₈,or a bromine-based gas such as HBr gas can be used as an etching gas.Further, an inert gas of He, Ar, Xe, or the like may be added asappropriate. Furthermore, O₂ gas or H₂ gas may be added to afluorine-based gas. In this embodiment mode, a mixed gas of C₄F₈ and Heis used for dry etching. The semiconductor layer 103 can be reduced inthickness by performing an alteration treatment on the semiconductorlayer 103 to form an insulating film on the surface of the semiconductorlayer 103 and then removing the insulating film 115. After etching, thesemiconductor layer 103 is reduced in thickness, and an end portion ofthe semiconductor layer comes to have curvature.

Next, as shown in FIG. 2D, an alteration treatment is further performedon the semiconductor layer 103 from which the insulating film 115 isremoved, to form the insulating film 104 on the surface of thesemiconductor layer 103. A method of performing the alteration treatmenton the semiconductor layer 103 to form the insulating film 104 issimilar to the case of forming the insulating film 115. By performingthe alteration treatment on the semiconductor layer 103 to form theinsulating film 104, the semiconductor layer 103 can be reduced inthickness even more, and the end portion of the semiconductor layer 103can have even more curvature.

Note that when the thickness of the island-shaped semiconductor layer103 is t (t>0) and the curvature radius of a cross-section of each ofthe end portions of the island-shaped semiconductor layer 103 is r(r>0), the relationship of t and r satisfies a conditional equation(t/2)≦r≦2t. Further, when the curvature radius of each of the endportions is r, a curvature center location 120 exists on a substrateside.

A thickness of the semiconductor layer 103 after being reduced inthickness is in the range of 0.5 nm to 200 nm inclusive, preferably 1 nmto 50 nm inclusive, and more preferably 1 nm to 10 nm inclusive.

Next, as shown in FIG. 2E, the insulating film 105 is formed over theinsulating film 102 b and the insulating film 104. The insulating film105 is formed by a CVD method, a sputtering method, an ALD method, orthe like, using silicon oxide, silicon nitride, silicon oxynitride,silicon nitride oxide, aluminum nitride, or the like. A thickness of theinsulating film 105 is in the range of 1 nm to 50 nm inclusive,preferably 1 nm to 20 nm inclusive, and more preferably 1 nm to 10 nminclusive.

The insulating film 104 and the insulating film 105 formed in the abovemanner can be used as a gate insulating film. Note that the insulatingfilm 104 can be used alone as the gate insulating film, or theinsulating film 105 can be used alone as the gate insulating film byforming the insulating film 105 after removing the insulating film 104.In this embodiment mode, the gate insulating film is to have astacked-layer structure of the insulating film 104 and the insulatingfilm 105. By performing the alteration treatment on the semiconductorlayer 103 and forming the insulating film 104 on the surface of thesemiconductor layer 103, coverage of the insulating film 104 that servesas the gate insulating film can be good. Further, the semiconductorlayer can be covered sufficiently even in a case where the insulatingfilms (the base insulating film) at a lower end portion of thesemiconductor layer or a periphery thereof is removed, due to an effectof a cleaning process using hydrofluoric acid or the like thataccompanies etching for processing the semiconductor layer into anisland shape and various processes. Consequently, a short circuitbetween the semiconductor layer and the gate insulating film, occurrenceof a leak current, electrostatic breakdown, or the like that stems froma defect in coverage by the gate insulating film at the end portions ofthe semiconductor layer can be prevented.

Next, as shown in FIG. 3A, the conductive layer 106 that serves as agate electrode is formed over the semiconductor layer 103 with theinsulating film 104 and the insulating film 105 therebetween. Theconductive layer 106 that serves as a gate electrode is formed byforming a conductive layer over an entire substrate by a CVD method or asputtering method using a conductive material, and then processing intoa desired shape by etching the conductive layer as selected. For theconductive material, a metal element such as tantalum, tungsten,titanium, molybdenum, chromium, aluminum, copper, or niobium; or analloy or compound material containing the metal element can be used. Inaddition, a semiconductor material typified by polycrystalline siliconto which an impurity element imparting one conductivity type such asphosphorus is added, can be used. The conductive layer 106 is formed asa single-layer structure or a stacked-layer structure using theseconductive materials. The conductive layer 106 that serves as a gateelectrode is formed to have a film thickness in the range of 50 nm to1000 nm inclusive, preferably 100 nm to 800 nm inclusive, and morepreferably 200 nm to 500 nm inclusive.

In this embodiment mode, as the conductive layer 106 that serves as agate electrode, a stacked-layer structure including a tantalum nitridelayer with a film thickness of 30 nm and a tungsten layer with a filmthickness of 370 nm is formed. By using an inductively coupled plasma(ICP) etching method and adjusting an etching condition as appropriate(such as an amount of electrical energy applied to a coil-shapedelectrode layer, an amount of electrical energy applied to an electrodelayer on a substrate side, or a temperature of an electrode on thesubstrate side), the conductive layer 106 can be etched such that across section thereof has a desired tapered form. In this embodimentmode, etching is performed on the tungsten layer using an etching gasincluding CF₄, Cl₂, and O₂, and ICP etching is performed on the tantalumnitride layer using an etching gas including SF₆, Cl₂, and O₂. Thetantalum nitride layer and the tungsten layer of the conductive layer106 may have widths that are roughly the same, or the conductive layer106 may have a slanted side surface. Further, a dry etching apparatusused in the present invention is not limited to an ICP etchingapparatus, and a parallel plate type etching apparatus, a microwaveetching apparatus, or an electron cyclotron resonance (ECR) etchingapparatus may be used. Note that a conductive layer (tantalum nitridelayer) of a lower layer may be formed to be wider than a conductivelayer of an upper layer (tungsten layer). Further, a sidewall may beformed in contact with a side surface of the gate electrode.

Next, as shown in FIG. 3B, an impurity element imparting oneconductivity type is added using the conductive layer 106 as a mask, toform the impurity regions 112 a and 112 b having one conductivity typeeach serving as a source region or a drain region. In addition, thechannel-forming region 111 is formed in the semiconductor layer 103. Theimpurity element imparting one conductivity type may be an impurityelement imparting n-type conductivity (for example, phosphorus, arsenic,or the like) or an impurity element imparting p-type conductivity (forexample, boron, aluminum, gallium, or the like). In this embodimentmode, phosphorus that is an impurity element imparting n-typeconductivity is used as the impurity element imparting one conductivitytype. Here, phosphorus is added to the impurity regions having oneconductivity type each serving as a source region or a drain region, sothat phosphorus is contained with a concentration of about 5×10¹⁹ to5×10²⁰/cm³.

Further, an LDD region may be included in each of the impurity regions112 a and 112 b in addition to the source region or drain region. TheLDD region may be formed so as to overlap with the gate electrode.

In addition, an impurity element imparting one conductivity type forcontrolling a threshold voltage of a transistor may be added to thechannel-forming region 111. By adding an impurity element with apredetermined concentration to the channel-forming region 111, thethreshold voltage of the transistor can be forced to shift to a desiredthreshold voltage. As the impurity element imparting one conductivitytype, an element imparting p-type conductivity such as boron, aluminum,or gallium, or an element imparting n-type conductivity such asphosphorus or arsenic can be used. In this embodiment mode, an elementimparting p-type conductivity can be used; for example, boron can beadded at a concentration of about 1×10¹⁶ cm⁻³ to 1×10¹⁸ cm⁻³. Note thatthe impurity element can be added to the channel-forming region 111before forming the conductive layer 106.

Note that after the impurity element imparting one conductivity type isadded to the semiconductor layer 103, a heat treatment is preferablyperformed to activate the impurity element that is added. The heattreatment can be performed using laser beam irradiation, RTA, or furnaceannealing. Specifically, the heat treatment may be performed in thetemperature range of 400° C. to 700° C. inclusive, preferably 500° C. to650° C. inclusive. Also, the heat treatment is preferably performed in anitrogen atmosphere. For example, activation can be carried out byperforming heating for four hours at 550° C.

Next, an interlayer insulating film is formed so as to cover theinsulating films and conductive layer provided over the substrate 101.In this embodiment mode, the interlayer insulating film is astacked-layer structure of the insulating film 107 and the insulatingfilm 108 (see FIG. 3B). Each of the insulating film 107 and theinsulating film 108 is formed by a CVD method, a sputtering method, anALD method, a coating method, or a combination method thereof, using aninorganic insulating material such as silicon oxide, silicon nitride,silicon oxynitride, or silicon nitride oxide; an insulating materialcontaining carbon such as diamond-like carbon (DLC); an organicinsulating material such as epoxy, polyimide, polyamide,polyvinylphenol, benzocyclobutene, or acrylic; or a siloxane materialsuch as siloxane resin. Note that the siloxane material refers to amaterial including a Si—O—Si bond. A skeleton structure of siloxaneincludes a bond between silicon and oxygen. As a substituent group, anorganic group containing at least hydrogen (for example, an alkyl groupor aromatic hydrocarbon) is used. As the substituent group, at least afluoro group may be used. Further, the insulating film 107 may be formedby forming an insulating film using a CVD) method, a sputtering method,an ALD method, or the like, and then performing a high-density plasmatreatment on the insulating film in an oxygen atmosphere or a nitrogenatmosphere. Note that here, although a two-layer stacked-layer structureof the insulating film 107 and the insulating film 108 is formed overthe gate electrode, the interlayer insulating film may have asingle-layer structure or a stacked-layer structure of three layers ormore. When the interlayer insulating film is to have a stacked-layerstructure, the insulating film in a lower layer (a side that is incontact with the gate electrode) is preferably formed using an inorganicinsulating material. In this embodiment mode, the insulating film 107 isformed by a CVD method using silicon nitride, and the insulating film108 is formed by applying siloxane on the insulating film 107.

Next, contacts holes (opening portions) that reach the semiconductorlayer 103 are formed in the insulating film 104, the insulating film105, the insulating film 107, and the insulating film 108 using a maskmade of a resist. Etching for forming the contact holes may be performedonce or a plurality of times depending on selectivity of the materialsused for the insulating films. The insulating film 104, the insulatingfilm 105, the insulating film 107, and the insulating film 108 areremoved by etching, and the contact holes that reach the source regionand the drain region can be formed. The etching may be wet etching ordry etching, or both may be employed. An etchant for the wet etching maybe a fluorine-based solution such as a mixed solution of ammoniumhydrogenfluoride and ammonium fluoride. As an etching gas, afluorocarbon gas typified by CHF₃, C₅F₈, C₄F₈, or the like; achlorine-based gas typified by Cl₂, BCl₃, SiCl₄, CCl₄, or the like; afluorine-based gas typified by CF₄, SF₆, NF₃, or the like; or O₂ can beused as appropriate. In addition, an inert gas may be added to theetching gas to be used. As the inert gas to be added, one or a pluralityof elements selected from He, Ne, Ar, Kr, and Xe can be used. In thisembodiment mode, the contact holes are formed by etching the insulatingfilm 107 and the insulating film 108 using CF₄, O₂, and He, andperforming ICP etching on the insulating film 104 and the insulatingfilm 105 using C₄F₈ and He.

Next, as shown in FIG. 3C, a conductive layer is formed so as to coverthe contact holes, and the conductive layer is etched to form theconductive layers 110 a and 110 b each functioning as a source electrodeor a drain electrode that is electrically connected with a portion ofthe source region or the drain region. The conductive layers 110 a and110 b can be formed by forming a conductive layer by a PVD method, a CVDmethod, an evaporation method, or the like, and then etching theconductive layer into a desired shape. Further, the conductive layer 110a and 110 b can be formed into a predetermined place as selected, by adroplet discharging method, a printing method, an electrolytic platingmethod, or the like. Furthermore, a reflow method or a damascene methodmay be used.

The conductive layers 110 a and 110 b each serving as a source electrodeor a drain electrode are formed to have a single-layer structure or astacked-layer structure of two layers or more by a CVD method or asputtering method, using a metal element selected from aluminum,tungsten, titanium, tantalum, molybdenum, nickel, platinum, copper,gold, silver, manganese, and neodymium, or an alloy material or compoundmaterial including the metal element. As an alloy material containingaluminum, a material mainly containing aluminum that contains nickel, oran alloy material mainly containing aluminum that contains nickel andone or both of carbon and silicon can be given. For the conductivelayers 110 a and 110 b, for example, a stacked-layer structure of abarrier layer, an aluminum silicon layer, and a barrier layer, or astacked-layer structure of a barrier layer, an aluminum silicon layer, atitanium nitride layer, and a barrier layer can be employed. Note thatthe barrier layer refers to a thin film made of titanium, a nitride oftitanium, molybdenum, or a nitride of molybdenum. Aluminum or aluminumsilicon is most suited as a material for forming the conductive layers110 a and 110 b because it has a low resistance value and isinexpensive. Further, when barrier layers of an upper layer and a lowerlayer are provided, diffusion of aluminum or aluminum silicon to thesemiconductor layer or occurrence of hillock can be prevented.

In this embodiment mode, for the conductive layers 110 a and 110 b, astacked-layer structure of a 60 nm thick titanium layer, a 40 nm thicktitanium nitride layer, a 300 nm thick aluminum layer, and a 100 nmthick titanium layer is formed and then ICP etching is performed on thestacked-layer structure using Cl₂ and BCl₃ to form a source electrodeand a drain electrode.

Accordingly, the thin film transistor 113 to which the present inventionis applied can be formed. Note that the structure of the transistorshown in this embodiment mode is one example, and the structure is notlimited to that shown in the figures.

In a semiconductor device manufactured by applying the presentinvention, a semiconductor layer is reduced in thickness, and achannel-forming region is formed in a region where the thickness isreduced. Consequently, since it is possible to reduce a sub-thresholdvalue and reduce a threshold voltage of a transistor, an operationcharacteristic of the semiconductor device can be improved. Further, bymaking an end portion of the semiconductor layer have curvature by athinning process of the semiconductor layer, coverage by an insulatingfilm formed over the semiconductor layer can be improved. Accordingly,since a defect stemming from the end portion of the semiconductor layercan be reduced, a semiconductor device with high reliability can bemanufactured. Therefore, a semiconductor device with enhancedperformance is possible.

Embodiment Mode 2

In this embodiment mode, an example of manufacturing a semiconductordevice is described with reference to FIGS. 4A to 6C, in which whenforming an insulating film on a semiconductor layer by performing analteration treatment, the insulating film is formed on a surface of thesemiconductor layer by a plasma treatment. Note that a description of astructure that is the same as in the above embodiment mode 1 issimplified and partially omitted.

Up through forming the island-shaped semiconductor layer 103 over thesubstrate 101 with the insulating films 102 a and 102 b therebetween isin accordance with the description made in the above embodiment mode 1about the substrate 101, the insulating films 102 a and 102 b, thesemiconductor layer 103, and the like; therefore, description thereof isomitted (see FIG. 5A).

As shown in FIG. 5B, an alteration treatment is performed on thesemiconductor layer 103 to form the insulating film 115 on the surfaceof the semiconductor layer 103. The insulating film 115 is formed byperforming a plasma treatment using a high-density plasma treatmentapparatus shown in FIGS. 4A and 4B. FIGS. 4A and 4B show one example ofa high-density plasma treatment apparatus, and a structure thereof isnot limited to that shown in the figures.

The high-density plasma treatment apparatus used in this embodiment modeis described below. As shown in FIG. 4A, the high-density plasmatreatment apparatus includes at least a first plasma treatment chamber201, a second plasma treatment chamber 202, a load lock chamber 203, anda common chamber 204. In the first plasma treatment chamber 201,oxidation by plasma treatment is performed, and in the second plasmatreatment chamber 202, nitridation by plasma treatment is performed.Each chamber in FIG. 4A is evacuated, and the oxidation by plasmatreatment and the nitridation by plasma treatment can be performedsuccessively without exposure to air. In additions to what is shown inFIG. 4A, the high-density plasma treatment apparatus may also include atleast one of a CVD chamber, a sputtering chamber, and a heat annealingchamber, which make it possible to successively perform film formationand a plasma treatment, and a plasma treatment and heat annealing,without exposure to air. Since a unit for generating a magnetic fieldsuch as a magnet or a coil is not provided in a periphery of the firstplasma treatment chamber 201 and the second plasma treatment chamber202, the apparatus can be simplified.

In the common chamber 204, a robot arm 205 is provided. In the load lockchamber 203, a cassette 206 which stores a plurality of the substrates101 shown in FIG. 5A is provided. One of the substrates 101 stored inthe cassette 206 can be carried by the robot arm 205 to the first plasmatreatment chamber 201 or the second plasma treatment chamber 202 throughthe common chamber 204. Further, by the robot arm 205, the substrate 101can be carried to the second plasma treatment chamber 202 from the firstplasma treatment chamber 201 through the common chamber 204, or thesubstrate 101 can be carried to the first plasma treatment chamber 201from the second plasma treatment chamber 202 through the common chamber204.

FIG. 4B shows a structure that is common between the first plasmatreatment chamber 201 and the second plasma treatment chamber 202. Toeach of the first plasma treatment chamber 201 and the second plasmatreatment chamber 202, a vacuum pump (not shown in figure) with whichpressure reduction to a certain pressure is possible is connected, andexhaust gas is discharged from an exhaust opening 210. Further, asubstrate holder 211 is provided for each of the first plasma treatmentchamber 201 and the second plasma treatment chamber 202, and thesubstrate 101 on which oxidation by plasma treatment or nitridation byplasma treatment is performed is held by the substrate holder 211. Thissubstrate holder 211 is also called a stage, and it is provided with aheater so that the substrate 101 can be heated. A gas such as oxygen,nitrogen, hydrogen, a rare gas, or ammonia is introduced into the plasmatreatment chamber from a gas introduction port as shown by arrows 212. Amicrowave 213 for exciting plasma is introduced through a wave-guidetube 215 that is provided over an antenna 214. The plasma is generatedin a region 217 shown by diagonal lines immediately below a dielectricplate 216 when pressure within the plasma treatment chamber afterintroducing the above gas is 5 Pa to 500 Pa, and the plasma is suppliedover the substrate 101 which is provided away from the region shown bythe diagonal lines. A shower plate 218 provided with a plurality ofholes may be provided as shown in FIG. 4B. The plasma that is obtainedin this plasma treatment chamber has an electron temperature of 1.5 eVor lower and an electron density of 1×10¹¹ cm⁻³ or higher; in otherwords, the plasma has a low electron temperature and a high electrondensity, and a plasma potential is 0 V to 5 V inclusive. Plasma metersregarding electron temperature, electron density, and plasma potentialcan be measured using a known method, for example a probe measuringmethod such as a double probe method.

In this embodiment mode, oxygen, hydrogen, and argon are introduced intothe first plasma treatment chamber 201 so that a flow ratio isO₂:H₂:Ar=1:1:100, and plasma is generated using a microwave with afrequency of 2.45 GHz. Although oxidation by plasma treatment ispossible without necessarily introducing hydrogen, it is preferable thata ratio of a flow amount of hydrogen to a flow amount of oxygen (H₂/O₂)is in the range of 0 to 1.5 inclusive. The flow amount of oxygen is setfor example in the range of 0.1 sccm to 100 sccm inclusive, and the flowamount of argon is set for example in the range of 100 sccm to 5000 sccminclusive. If hydrogen is introduced, the flow amount of hydrogen is setfor example in the range of 0.1 sccm to 100 sccm inclusive. A differentrare gas may be introduced instead of argon. Pressure within the firstplasma treatment chamber 201 is set at an appropriate value in the rangeof 5 Pa to 500 Pa inclusive. The substrate 101 is set on the substrateholder 211 in the first plasma treatment chamber 201, and a temperatureof the heater provided to the substrate holder 211 is maintained at 400°C. Then, oxidation by plasma treatment is performed on the semiconductorlayer 103 over the substrate 101. In this embodiment mode, as apparentfrom FIG. 5B, a portion of the base insulating film that is not coveredby the semiconductor layer 103 is also oxidized by the plasma treatment.However, in a case where the base insulating film is made of an oxide,an oxide film is not formed on a surface of the base insulating filmeven when oxidation by plasma treatment is performed.

By the above oxidation by plasma treatment, the insulating film 115 madeof an oxide film, as shown in FIG. 5B, is formed on the surface of thesemiconductor layer 103 so as to have a thickness of 20 nm or less. Inthe insulating film 115, argon that is introduced to the first plasmatreatment chamber 201 is included at a predetermined concentration, forexample, 1×10¹⁵ atoms/cm³ to 1×10¹⁶ atoms/cm³ inclusive. In forming theinsulating film 115, the thickness of the insulating film formed at theend portion of the semiconductor layer 103 does not become thinner thanother portions. Further, at that end portion, the insulating film 115does not crack either. In a case of using a plastic substrate with heatresistance instead of a glass substrate, the temperature of the heaterprovided to the substrate holder 211 is maintained at 250° C., forexample.

Since the plasma over the semiconductor layer 103 has an electrontemperature of 1.5 eV or lower and an electron density of 1×10¹¹ cm⁻³ orhigher, and since a region where plasma is generated is away from thesemiconductor layer, plasma damage to the insulating film due to theoxidation by plasma treatment is suppressed. By using a microwave of2.45 GHz for generating plasma instead of that with a frequency of 13.56MHz, low electron temperature and high electron density can be realizedeasily. Further, if low electron temperature and high electron densitycan be obtained, a method other than using the microwave of 2.45 GHz maybe employed.

As shown in FIG. 5C, the insulating film 115 formed by the plasmatreatment is removed. A method of removing the insulating film 115 canbe dry etching or wet etching. For example, in a case of performing dryetching, a fluorocarbon-based gas such as CHF₃, C₅F₈, or C₄F₈; achlorine-based gas such as Cl₂, BCl₃, or SiCl₄; a fluorine-based gassuch as CF₄, NF₃, or SF₆; or HBr gas can be used as an etching gas.Further, an inert gas of He, Ar, Xe, or the like may be added asappropriate. Furthermore, O₂ gas may be added to a fluorine-based gas.By removing the insulating film 115 that is formed by performing plasmatreatment on the semiconductor layer 103, the semiconductor layer 103can be reduced in thickness. After etching, the semiconductor layer 103is reduced in thickness, and the end portion of the semiconductor layerhas curvature. In this embodiment mode, ICP etching is performed usingC₄F₈, and He.

Next, as shown in FIG. 5D, a plasma treatment is performed on thesemiconductor layer 103 to form an insulating film 116 on a surface ofthe semiconductor layer 103. A method of oxidation by plasma treatmentperformed on the semiconductor layer 103 is the same method used whenforming the insulating film 115. By forming the insulating film 116 byperforming the plasma treatment on the semiconductor layer 103, thesemiconductor layer 103 can be reduced in thickness even more. Theinsulating film 116 can be used as a gate insulating film.

The insulating film 116 may be made into a silicon oxynitride film byperforming nitridation by plasma treatment in the second plasmatreatment chamber 202, and the silicon oxynitride film may be used as agate insulating film. When performing nitridation by plasma treatment,nitrogen and argon are used as gasses introduced to the second plasmatreatment chamber 202, and the temperature of the glass substrate is tobe the same as that when the above-mentioned oxidation by plasmatreatment is performed. Hydrogen may also be introduced in addition tonitrogen and argon, and argon may be replaced with another rare gas.Further, instead of nitrogen, a gas used when nitridation is performedby a heat treatment at high temperature, such as ammonia or N₂O can beused. The insulating film 116 includes the rare gas introduced into thesecond plasma treatment chamber 202 at a predetermined concentration.

Nitridation by plasma treatment may be performed on the semiconductorlayer 103 in the second plasma treatment chamber 202 first to form anitride film. Further, oxidation by plasma treatment may be performed onthe nitride film in the first plasma treatment chamber 201.

In an example of an insulating film that is formed by a high-densityplasma treatment using the apparatus shown in FIGS. 4A and 4B, a siliconoxide layer with a thickness of 3 nm to 6 nm inclusive is formed on asurface of the semiconductor layer 103 by a plasma treatment in anatmosphere containing oxygen, and then a surface of the silicon oxidelayer is treated with nitrogen plasma in an atmosphere containingnitrogen to form a nitrogen-plasma treated layer Specifically, a siliconoxide layer with a thickness of 3 nm to 6 nm inclusive is first formedon the surface of the semiconductor layer 103 by a plasma treatment inan atmosphere containing oxygen. Then, a nitrogen-plasma treated layerwith a high nitrogen concentration is provided on the surface of thesilicon oxide layer or in a periphery of the surface, by performing aplasma treatment in an atmosphere containing nitrogen. Note that theperiphery of the surface refers to the silicon oxide layer from thesurface to a depth in the range of 0.5 nm to 1.5 nm inclusive. Forexample, by performing the plasma treatment in an atmosphere containingnitrogen, a structure becomes that in which nitrogen is contained at aratio of 20 atomic % to 50 atomic % inclusive in a region of the siliconoxide layer from the surface to about 1 nm in depth perpendicular to thesurface. Further, a surface of the insulating film can be oxidized ornitrided by a high-density plasma treatment.

For example, by forming a silicon layer as the semiconductor layer 103and oxidizing a surface of the silicon layer by plasma treatment, adense oxide film that does not warp at an interface with thesemiconductor layer 103 can be formed. Further, by nitriding the oxidefilm by plasma treatment to form a nitride film by substituting oxygenin a surface layer portion with nitrogen, an insulating layer can beeven denser. In this manner, an insulating film with high withstandvoltage can be formed.

In any case, by using a solid phase oxidation treatment or a solid phasenitridation treatment by plasma treatment as described above, even whena glass substrate with an allowable temperature limit of 700° C. isused, an insulating film can be obtained that is equal to an insulatingfilm that is formed by a thermal oxidation treatment with a temperaturerange of 950° C. to 1050° C. inclusive. In other words, as asemiconductor element, in particular as an insulating film that servesas a gate insulating film of a thin film transistor or a non-volatilestorage element, an insulating film with high reliability can be formed.

In this manner, by performing oxidation, nitridation and the like byplasma treatment on the semiconductor layer 103, the insulating film 116is formed. Since the thickness of the semiconductor layer 103 becomesthin depending on the thickness of the insulating film that is formed,the semiconductor layer 103 can be reduced in thickness. Further, theinsulating film 116 that is formed can be used as a gate insulatingfilm.

As shown in FIG. 5E, after the insulating film 116 is formed, a siliconnitride film or a silicon nitride film containing oxygen may be formedas an insulating film 117 by a CVD method or the like so that a gateinsulating film is formed along with the insulating film 116.Consequently, oxidation of a gate electrode and a wiring that extendsfrom the gate electrode that are formed later, which occurs by cominginto contact with the insulating film that is made of an oxide film, canbe suppressed. Further, nitridation by plasma treatment at a lowelectron temperature and high electron density may be performed on theabove silicon nitride film or the silicon nitride film containingoxygen, for a purpose of densification or the like.

Note that the insulating film 116 can be used as a gate insulating filmas a single layer, or the insulating film 117 can be used as a gateinsulating film as a single layer by forming the insulating film 117after removing the insulating film 116. In this embodiment mode, astacked-layer structure of the insulating film 116 and the insulatingfilm 117 is employed.

Next, a conductive layer used as a gate electrode is formed over theinsulating film 116 and the insulating film 117. The conductive layer isto have a thickness of 100 nm to 500 nm inclusive. The conductive layercan be formed by a sputtering method, an evaporation method, or a CVDmethod. The conductive layer may be formed of an element selected fromtantalum, tungsten, titanium, molybdenum, aluminum, copper, chromium,and neodymium; or an alloy material or a compound material mainlycontaining the element. Alternatively, a semiconductor layer typified bya polycrystalline silicon film doped with an impurity element such asphosphorus, or an AgPdCu alloy layer may be used for the conductivelayer. The conductive layer may have a single-layer structure or astacked-layer structure with two or more layers. For example, in a caseof forming a three-layer structure, a 50 nm thick tungsten film as afirst conductive layer, a 500 nm thick aluminum-silicon (Al—Si) alloyfilm as a second conductive film, and a 30 nm thick titanium nitridefilm as a third conductive layer may be stacked in this order.Alternatively, a tungsten nitride film may be used instead of thetungsten film in the first conductive layer, an aluminum-titanium(Al—Ti) alloy film may be used instead of the aluminum-silicon (Al—Si)alloy film in the second conductive layer, and a titanium film may beused instead of titanium nitride film in the third conductive layer.

Next, as shown in FIG. 6A, a mask made of a resist is formed, theconductive layer is processed into a desired shape, and the conductivelayer 106 that serves as a gate electrode layer is formed. Note that asan etching gas, a chlorine-based gas typified by Cl₂, BCl₃, SiCl₄, orCCl₄; a fluorine-based gas typified by CF₄, SF₆, or NF₃; or O₂ can beused as appropriate.

Although in this embodiment mode, an example is shown in which a gateelectrode is formed to have a side surface that is perpendicular to asubstrate, the present invention is not limited thereto. For example,both the first conductive layer and the second conductive layer may havea tapered shape when seen from a cross section, or one of the firstconductive layer and the second conductive layer may have a surface thatis perpendicular to the substrate by anisotropic etching. A taper anglemay be different or the same between the conductive layers that arestacked. By having a tapered shape, coverage by a film that is stackedthereover improves, and reliability improves because defects arereduced.

Next, as shown in FIG. 6B, an impurity element imparting oneconductivity type is added using the conductive layer as a mask, to formthe impurity regions 112 a and 112 b having one conductivity type eachserving as a source region or drain region. Also, the channel-formingregion 111 is formed in the semiconductor layer. Specifically, theformation method of the impurity regions shown in the embodiment mode 1can be applied.

Next, an interlayer insulating film is formed so as to cover theinsulating films and conductive layer provided over the substrate 101.In this embodiment mode, the interlayer insulating film is astacked-layer structure of the insulating film 107 and the insulatingfilm 108. Specifically, the formation method of the interlayerinsulating film shown in the embodiment mode 1 can be applied.

Next, contact holes (opening portions) that reach the semiconductorlayer 103 are formed in the insulating film 107, the insulating film108, the insulating film 116, and the insulating film 117, using a maskmade of a resist. Specifically, the formation method of the contactholes shown in the embodiment mode 1 can be applied.

Next, as shown in FIG. 6C, a conductive layer is formed so as to coverthe contact holes, and the conductive layer is etched to form theconductive layers 110 a and 110 b each functioning as a source electrodeor a drain electrode that is electrically connected with a portion ofthe source region or the drain region. Specifically, the formationmethod of the conductive layers 110 a and 110 b shown in the embodimentmode 1 can be applied.

Accordingly, a thin film transistor to which the present invention isapplied can be formed. Note that the structure of the transistor shownin this embodiment mode is one example, and the structure is not limitedto that shown in the figures.

A characteristic of this embodiment mode, as described above, is toperform a plasma treatment with plasma of a low electron temperature andhigh electron density on a semiconductor layer in order to form a gateinsulating film of a thin film transistor. The gate insulating filmaccording to this embodiment mode is one for which plasma damage andcrack occurrence are suppressed, and it can be formed at a temperaturethat does not affect the glass substrate.

In a semiconductor device according to this embodiment mode, asemiconductor layer is reduced in thickness, and a channel-formingregion is formed in a region where the thickness is reduced.Consequently, since it is possible to reduce a sub-threshold value andreduce a threshold voltage of a transistor, an operation characteristicof the semiconductor device can be improved. Further, by making an endportion of the semiconductor layer have curvature along with a thinningprocesses of the semiconductor layer, coverage by an insulating filmformed over the semiconductor layer can be improved. Accordingly, sincea defect stemming from the end portion of the semiconductor layer can bereduced, a semiconductor device with high reliability can bemanufactured. Therefore, a semiconductor device with enhancedperformance is possible.

Note that this embodiment mode can be combined with the embodiment mode1.

Embodiment Mode 3

In this embodiment mode, an example of manufacturing a semiconductordevice by a different method from those of the above embodiment modes 1and 2 is described with reference to 7A to 8D. Hereinafter, structuresthat are the same as those in the embodiment modes 1 and 2 are denotedby the same reference numerals and description thereof is omitted.

As shown in FIG. 7A, up through forming the island-shaped semiconductorlayer 103 over the substrate 101 with the insulating films 102 a and 102b therebetween is in accordance with the description made in the aboveembodiment modes 1 and 2 about the substrate 101, the insulating films102 a and 102 b, the semiconductor layer 103, and the like; therefore,description thereof is omitted.

Next, as shown in FIG. 7B, the insulating film 115 is formed on asurface of the semiconductor layer 103 by performing an alterationtreatment on the semiconductor layer 103. A desired treatment may beperformed in a region of the semiconductor layer 103 where theinsulating film 115 is to be formed. Specifically, a thermal oxidationtreatment, a treatment with a solution that has strong oxidative powersuch as ozone water, a plasma treatment, or the like is performed on asurface of the semiconductor layer 103, so that an oxide of thesemiconductor layer 103 is formed on the semiconductor layer 103. Thisalso applies to cases of forming a nitride, an oxynitride, and a nitrideoxide of the above semiconductor layer 103. Note that by performing aplasma treatment on the semiconductor layer, controlling a thickness ofthe insulating film 115 becomes easy.

Next, as shown in FIG. 7C, the insulating film 115 is removed byetching. A method of removing the insulating film 115 may be dry etchingor wet etching. For example, in a case of performing dry etching,chlorine-based gas such as Cl₂, BCl₃, or SiCl₄, a fluorine-based gassuch as CF₄, NF₃, or SF₆, or HBr gas can be used as an etching gas.Further, an inert gas of He, Ar, Xe, or the like may be added asappropriate. Furthermore, O₂ gas may be added to a fluorine-based gas.When the insulating film 115 is etched, the insulating film 102 b isalso removed in a manner that digs in under the semiconductor layer 103.

Next, as shown in FIG. 7D, an alteration treatment is further performedon the semiconductor layer 103 from which the insulating film 115 isremoved, to form the insulating film 118 on the surface of thesemiconductor layer 103. A method of performing the alteration treatmenton the semiconductor layer 103 to form the insulating film 118 is thesame as in the case of forming the insulating film 115. By performingthe alteration treatment on the semiconductor layer 103 to form theinsulating film 118, the semiconductor layer 103 can be reduced inthickness even more, and an upper end portion and a lower end portion ofthe semiconductor layer 103 can have even more curvature.

Next, as shown in FIG. 7E, the insulating film 118 is removed byetching. A method of removing the insulating film 118 is the same methodof removing the insulating film 115.

Next, as shown in FIG. 7F, an alteration treatment is performed on thesemiconductor layer 103 to form an insulating film 119 on a surface ofthe semiconductor layer 103. A method of forming the insulating film 119by performing an alteration treatment on the semiconductor layer 103 isthe same method as the methods for forming the insulating films 115 and118. The insulating film 119 formed in this manner can be used as a gateinsulating film.

Note that when a thickness of the semiconductor layer 103 is t (t>0) anda curvature radius of a cross-section of each of the end portions of thesemiconductor layer 103 is r (r>0), the relationship of t and rsatisfies a conditional equation (t/4)≦r≦t.

Further, as shown in FIG. 8A, the insulating film 105 can be formed overthe entire substrate. The insulating film 105 is formed by a CVD methodor a sputtering method using a material such as silicon oxide, siliconnitride, silicon oxynitride, silicon nitride oxide, SiOF, SiOC, DLC, orporous silica. Note that the insulating film 105 may be formed over thesemiconductor layer 103 without forming the insulating film 119.Alternatively, the insulating film 105 may be formed after removing theinsulating film 119. By forming the insulating film 105, lower-end rimportions of the semiconductor layer 103 are covered by the insulatingfilm 105, which alleviates concentration of an electric field in thoseportions. Further, upper end portions of the semiconductor layer alsohave curvature. By performing an alteration treatment on thesemiconductor layer to form an insulating film on a surface of thesemiconductor layer, coverage by the insulating film becomes good.

Next, the conductive layer 106 that serves as a gate electrode is formedover the semiconductor layer 103 with the insulating film 119 and theinsulating film 105 interposed therebetween. An impurity elementimparting one conductivity type is added to the semiconductor layer 103using the conductive layer 106 as a mask, to form the channel-formingregion 111 and the impurity regions 112 a and 112 b each serving as asource region or a drain region (see FIG. 8B).

The conductive layer 106 can be formed using a metal element such astantalum, tungsten, titanium, molybdenum, chromium, aluminum, copper, orniobium, or an alloy material or a compound material containing themetal element. Alternatively, the conductive layer can be formed using asemiconductor material typified by polycrystalline silicon to which animpurity element imparting one conductivity type such as phosphorus isadded. The conductive layer 106 serving as a gate electrode can beformed as a single-layer structure or a stacked-layer structure usingone or a plurality of these materials. A thickness of the conductivelayer 106 is formed in a range of 100 nm to 1000 nm inclusive,preferably 200 nm to 800 nm inclusive, and more preferably 300 nm to 500nm inclusive. Further, the conductive layer 106 that serves as a gateelectrode may be formed over an entire surface by a CVD method or asputtering method using the above material and then processed into adesired shape by selective etching.

Next, an impurity element imparting one conductivity type is added usingthe conductive layer 106 as a mask, to form the impurity regions 112 aand 112 b having one conductivity type each serving as a source regionor a drain region. Further, the channel-forming region 111 is formed inthe semiconductor layer. Specifically, the formation method of theimpurity regions 112 a and 112 b shown in the embodiment mode 1 can beapplied.

Next, as shown in FIG. 5C, an interlayer insulating film is formed so asto cover the insulating films and conductive layer provided over thesubstrate 101. In this embodiment mode, the interlayer insulating filmhas a stacked-layer structure of the insulating film 107 and theinsulating film 108. Specifically, the formation method of theinterlayer insulating film shown in the embodiment mode 1 can beapplied.

Next, as shown in FIG. 8D, using a mask made of a resist, contact holes(opening portions) that reach the semiconductor layer 103 is formed inthe insulating film 119, the insulating film 105, the insulating film107, and the insulating film 108. Specifically, the formation method ofthe contact holes shown in the embodiment mode 1 can be applied.

Then, a conductive layer is formed so as to cover the contact holes, andthe conductive layer is etched to form the conductive layers 110 a and110 b each functioning as a source electrode or a drain electrode thatis electrically connected with portion of the source region or the drainregion. Specifically, the formation method of the conductive layers 110a and 110 b shown in the embodiment mode 1 can be applied.

By the above process, a semiconductor device containing a thin filmtransistor can be manufactured (see FIG. 8D).

In a semiconductor device according to this embodiment mode, asemiconductor layer is reduced in thickness, and a channel-formingregion is formed in a region where the thickness is reduced.Consequently, since it is possible to reduce a sub-threshold value andreduce a threshold voltage of a transistor, an operation characteristicof the semiconductor device can be improved. Further, by making an endportion of the semiconductor layer have curvature by a thinning processof the semiconductor layer, coverage by an insulating film formed overthe semiconductor layer can be improved. Accordingly, since a defectstemming from the end portion of the semiconductor layer can be reduced,a semiconductor device with high reliability can be manufactured.Therefore, a semiconductor device with enhanced performance is possible.

Embodiment Mode 4

A semiconductor device according to the present invention can be appliedto an integrated circuit such as a central processing unit (CPU). Inthis embodiment mode, an example of a CPU to which the semiconductordevice described in the above embodiment modes 1 to 3 is described belowwith reference to drawings.

A CPU 3660 shown in FIG. 9 mainly includes over a substrate 3600 anarithmetic logic unit (ALU) 3601, an ALU controller 3602, an instructiondecoder 3603, an interrupt controller 3604, a timing controller 3605, aregister 3606, a register controller 3607, a bus interface (Bus I/F)3608, a rewritable ROM 3609, and a ROM interface (ROM I/F) 3620.Alternatively, the ROM 3609 and the ROM interface 3620 may be providedover a different chip. Such various circuits included in the CPU 3660can be formed by using the thin film transistor described in any of theembodiment modes 1 to 3, or a CMOS transistor, an nMOS transistor, apMOS transistor, or the like formed by combining the thin filmtransistors.

Note that the CPU 3660 shown in FIG. 9 is merely one example that isshown with a simplified structure, and an actual CPU has a variety ofstructures depending on usage. Therefore, a structure of the CPU towhich the present invention is applied is not limited to that shown inFIG. 9.

An instruction input to the CPU 3660 through the bus interface 3608 isinput to the instruction decoder 3603 and decoded, and then input to theALU controller 3602, the interrupt controller 3604, the registercontroller 3607, and the timing controller 3605.

The ALU controller 3602, the interrupt controller 3604, the registercontroller 3607, and the timing controller 3605 perform various controlsbased on a decoded instruction. Specifically, the ALU controller 3602generates a signal to control driving of the ALU 3601. The interruptcontroller 3604 judges an interruption request from an input/outputdevice outside or a peripheral circuit based on priority or a mask stateand processes the interruption request, during program execution of theCPU 3660. The register controller 3607 generates an address of theregister 3606, and performs reading or writing in the register 3606depending on a state of the CPU.

Further, the timing controller 3605 generates a signal to controldriving timing of the ALU 3601, the ALU controller 3602, the instructiondecoder 3603, the interrupt controller 3604, and the register controller3607. For example, the timing controller 3605 is provided with aninternal clock generator that generates an internal clock signal CLK 2(3622) based on a reference clock signal CLK 1 (3621), and supplies theinternal clock signal CLK 2 to each of the above circuits.

FIG. 10 shows a display device in which a pixel portion, a CPU, andother circuits are formed over one substrate, in other words asystem-on-panel. Over a substrate 3700, a pixel portion 3701, a scanline driver circuit 3702 that selects a pixel included in the pixelportion 3701, and a signal line driver circuit 3703 that supplies avideo signal to a selected pixel are provided. The CPU 3704 and anothercircuit, for example the control circuit 3705, are connected by wiresthat extend from the scan line driver circuit 3702 and the signal linedriver circuit 3703. Note that an interface is included in the controlcircuit 3705. Further, a connection portion to an FPC terminal isprovided at an end portion of the substrate 3700 to performcommunication with an external signal.

As the other circuit, a video signal processing circuit, a power sourcecircuit, a gray scale power source circuit, a video RAM, a memory (DRAM,SRAM, PROM) or the like can be provided in addition to the controlcircuit 3705. The other circuit may be included in an IC chip and thenmounted on the substrate. In addition, the scan line driver circuit 3702and the signal line driver circuit 3703 do not necessarily have to beformed over the same substrate. For example, just the scan line drivercircuit 3702 may be formed over the same substrate and the signal linedriver circuit 3703 may be included in an IC chip and then mounted.

Note that although in this embodiment mode, an example of applying thesemiconductor device according to the present invention to a CPU isdescribed, the present invention is not limited thereto. For example,the semiconductor device according to the present invention can beapplied to a pixel portion, a driver circuit portion, and the like of adisplay device provided with an organic light-emitting element, aninorganic light-emitting element, a liquid crystal element, or the like.Other than that, by applying the present invention, a digital camera; asound reproduction device such as a car stereo system; an imagereproduction device provided with a recording medium such as a laptopcomputer, a game machine, a portable information terminal (such as aportable phone or a portable game machine), or a domestic game machine;or the like can be manufactured.

A semiconductor device to which the present invention is applied canhave good electrical characteristics of a conductive layer and asemiconductor layer. Accordingly, reliability of the semiconductordevice can be improved.

Embodiment Mode 5

In this embodiment mode, one example of a usage mode of thesemiconductor device described in the preceding embodiment modes will bedescribed. Specifically, an application example of a semiconductordevice to/from which data can be input/output without contact will bedescribed below with reference to the drawings. The semiconductor deviceto/from which data can be input/output without contact is also called anRFID tag, an ID tag, an IC tag, an IC chip, an RFID tag, a wireless tag,an electronic tag, or a wireless chip depending on the usage mode.

One example of a top structure of a semiconductor device described inthis embodiment mode is described with reference to FIG. 11A. Asemiconductor device 2180 shown in FIG. 11A includes a thin filmintegrated circuit 2131 including a plurality of elements such as thinfilm transistors for forming a memory portion and a logic portion, and aconductive layer 2132 which serves as an antenna. The conductive layer2132 which serves as an antenna is electrically connected to the thinfilm integrated circuit 2131. The semiconductor device according to thepresent invention described in any of the embodiment modes 1 to 4 can beapplied to the thin film integrated circuit 2131.

Schematic cross-sectional views of FIG. 11A are shown in FIGS. 11B and11C. The conductive layer 2132 which serves as an antenna is providedabove the elements for forming the memory portion and the logic portion.For example, the conductive layer 2132 which serves as an antenna can beprovided above the thin film integrated circuit 2131 with an insulatingfilm 2130 interposed therebetween (see FIG. 11B). Alternatively, theconductive layer 2132 which serves as an antenna may be provided over asubstrate 2133 and then the substrate 2133 and the thin film integratedcircuit 2131 may be attached to each other so as to sandwich theconductive layer 2132 (see FIG. 11C). The example in which a conductivelayer 2136 provided over the insulating film 2130 and the conductivelayer 2132 which serves as an antenna are electrically connected to eachother with conductive particles 2134 contained in an adhesive resin 2135is shown in FIG. 11C.

Note that in this embodiment mode, although the example in which theconductive layer 2132 which serves as an antenna is provided in theshape of a coil and either an electromagnetic induction method or anelectromagnetic coupling method is employed is described, thesemiconductor device of the present invention is not limited thereto,and a microwave method may be employed as well. In the case of amicrowave method, the shape of the conductive layer 2132 which serves asan antenna may be decided as appropriate depending on the wavelength ofan electromagnetic wave.

For example, when the microwave method (e.g., with an UHF band (in therange of 860 to 960 MHz inclusive), a frequency band of 2.45 GHz, or thelike) is employed as the signal transmission method of the semiconductordevice 2180, the shape such as the length of the conductive layer 2132which serves as an antenna may be set as appropriate in consideration ofthe wavelength of an electromagnetic wave used in sending a signal. Forexample, the conductive layer 2132 which serves as an antenna can beformed into a shape of a line (e.g., a dipole antenna (see FIG. 12A)),into a flat shape (e.g., a patch antenna (see FIG. 12B)), into a shapeof a ribbon (FIGS. 12C and 12D), or the like. Further, the shape of theconductive layer 2132 which serves as an antenna is not limited to aline, and the conductive layer in the shape of a curved line, in anS-shape, or in a shape combining them may be provided as well inconsideration of the wavelength of the electromagnetic wave.

The conductive layer 2132 which serves as an antenna is formed of aconductive material by a CVD method, a sputtering method, a printingmethod such as a screen printing method or a gravure printing method, adroplet discharging method, a dispenser method, a plating method, or thelike. As the conductive material, a metal element such as aluminum,titanium, silver, copper, gold, platinum, nickel, palladium, tantalum,molybdenum, or the like, or an alloy material or a compound materialmainly containing the element is used, and the conductive layer 2132employs a single-layer structure or a stacked-layer structure.

For example, when the conductive layer 2132 which serves as an antennais formed by a screen printing method, it can be provided by selectivelyprinting a conductive paste in which conductive particles with a graindiameter of several nm to several tens of μm are dissolved or dispersedin an organic resin. As the conductive particle, at least one of metalparticles such as silver, gold, copper, nickel, platinum, palladium,tantalum, molybdenum, titanium, and the like; fine particles of silverhalide; or dispersive nanoparticles can be used. Further, as the organicresin included in the conductive paste, at least one of organic resinswhich function as a binder, a solvent, a dispersing agent, and a coatingmaterial of metal particles can be used. Typically, an organic resinsuch as an epoxy resin and a silicon resin can be given as an example.Further, in forming the conductive layer 2132, it is preferable to bakethe conductive paste after providing it. For example, in the case ofusing fine particles (e.g., with a grain diameter of 1 to 100 nm,inclusive) mainly containing silver as a material of the conductivepaste, the conductive layer 2132 can be formed by baking the conductivepaste at a temperature in the range of 150 to 300° C. inclusive toharden it. Alternatively, fine particles mainly containing solder orlead-free solder may be used. In this case, fine particles with a graindiameter of less than or equal to 20 μm are preferably used. Solder andlead-free solder have the advantage of low cost.

Next, an operation example of the semiconductor device according to thisembodiment mode is described with reference to FIG. 13A.

The semiconductor device 2180 shown in FIG. 13A has a function ofexchanging data without contact, and includes a high-frequency circuit81, a power source circuit 82, a reset circuit 83, a clock generatingcircuit 84, a data demodulating circuit 85, a data modulating circuit86, a control circuit 87 for controlling other circuits, a memorycircuit 88, and an antenna 89. The high-frequency circuit 81 is acircuit that receives a signal from the antenna 89, and outputs a signalthat is received from the data modulating circuit 86 through the antenna89. The power source circuit 82 is a circuit that generates a powersource potential from a received signal. The reset circuit 83 is acircuit that generates a reset signal. The clock generating circuit 84is a circuit that generates various clock signals based on a receivedsignal input from the antenna 89. The data modulating circuit 86 is acircuit that modulates a signal received from the control circuit 87. Asthe control circuit 87, for example, a code extracting circuit 91, acode judging circuit 92, a CRC judging circuit 93, and an output unitcircuit 94 are provided. Note that the code extracting circuit 91extracts each of a plurality of codes included in an instruction sent tothe control circuit 87. The code judging circuit 92 judges the contentof the instruction by comparing each extracted code with a codecorresponding to a reference. The CRC judging circuit 93 detects whetheror not there is a transmission error or the like based on a judged code.In FIG. 13A, in addition to the control circuit 87, the high-frequencycircuit 81 and the power source circuit 82 which are analog circuits areincluded.

Next, one example of an operation of the aforementioned semiconductordevice is described. First, a wireless signal is received by the antenna89 and then sent to the power source circuit 82 through thehigh-frequency circuit 81, so that a high power source potential(hereinafter referred to as “VDD”) is generated. VDD is supplied to eachcircuit in the semiconductor device 2180. A signal sent to the datademodulating circuit 85 through the high-frequency circuit 81 isdemodulated (hereinafter this signal is called a “demodulated signal”).Moreover, signals that passes through the reset circuit 83 and the clockgenerating circuit 84 through the high-frequency circuit 81, and thedemodulated signal are sent to the control circuit 87. The signals sentto the control circuit 87 are analyzed by the code extracting circuit91, the code judging circuit 92, the CRC judging circuit 93, and thelike. Then, based on the analyzed signals, information of thesemiconductor device stored in the memory circuit 88 is output. Theoutput information of the semiconductor device is encoded through theoutput unit circuit 94. Further, the encoded information of thesemiconductor device 2180 passes through the data modulating circuit 86and then is sent by the antenna 89 as a wireless signal. Note that a lowpower source potential (hereinafter called “VSS”) is common in theplurality of circuits included in the semiconductor device 2180 and GNDcan be used as VSS.

In this manner, by sending a signal from a communication unit (e.g., areader/writer or a unit having a function of a reader or a writer) tothe semiconductor device 2180 and receiving a signal sent from thesemiconductor device 2180 by the reader/writer, data of thesemiconductor device can be read.

Further, in the semiconductor device 2180, a power source voltage may besupplied to each circuit by electromagnetic waves without providing apower source (a battery), or a power source (battery) may be provided sothat a power source voltage is supplied to each circuit by bothelectromagnetic waves and the power source (battery).

Next, one example of usage modes of the semiconductor device to/fromwhich data can be input/output without contact is described. The sidesurface of a mobile terminal including a display portion 3210 isprovided with a communication unit 3200, and the side surface of aproduct 3220 is provided with a semiconductor device 3230 (see FIG.13B). Note that the communication unit 3200 has a function of readingand transmitting a signal like a reader/writer, or has only a functionof reading a signal or transmitting a signal. When the communicationunit 3200 is held over the semiconductor device 3230 included in theproduct 3220, the display portion 3210 displays information on theproduct, such as a raw material, a place of origin, an inspection resultfor each production step, a history of distribution process, descriptionof the product, or the like. Further, while a product 3260 istransferred by a conveyer belt, the product 3260 can be inspected byusing a reader/writer 3240 and a semiconductor device 3250 provided forthe product 3260 (see FIG. 13C). As the semiconductor devices 3230 and3250, the aforementioned semiconductor device 2180 can be applied. Inthis manner, by using the semiconductor device according to the presentinvention in the system, information can be obtained easily and higherperformance and a high added value are achieved. Further, since thesemiconductor device according to the present invention has highreliability, a malfunction or the like of a semiconductor deviceprovided for a product can be prevented.

Note that an applicable range of the semiconductor device according tothe present invention is wide in addition to the above, and thesemiconductor device can be applied to any product as long as itclarifies information of an object, such as the history thereof, withoutcontact and is useful for production, management, or the like. Forexample, the semiconductor device can be provided for bills, coins,securities, certificates, bearer bonds, packing containers, books,recording media, personal belongings, vehicles, food, clothing, healthproducts, commodities, medicine, electronic devices, and the likeExamples of them are described with reference to FIGS. 14A to 14H.

The bills and coins are money distributed to the market, and include onevalid in a certain area (a cash voucher), memorial coins, and the like.The securities refer to checks, certificates, promissory notes, and thelike (see FIG. 14A). The certificates refer to driver's licenses,certificates of residence, and the like (see FIG. 14B). The bearer bondsrefer to stamps, rice coupons, various gift certificates, and the like(see FIG. 14C). The packing containers refer to wrapping paper for foodcontainers and the like, plastic bottles, and the like (see FIG. 14D).The books refer to hardbacks, paperbacks, and the like (see FIG. 14E).The recording media refer to DVD software, video tapes, and the like(see FIG. 14F). The vehicles mean a wheeled vehicle such as a bicycle, avessel and the like (see FIG. 14G). The personal belongings refer tobags, glasses, and the like (see FIG. 14H). The food refers to foodarticles, drink, and the like. The clothing refers to clothes, footwear,and the like. The health products refer to medical instruments, healthinstruments, and the like. The commodities refer to furniture, lightingequipment, and the like. The medicine refers to medical products,pesticides, and the like. The electronic devices refer to liquid crystaldisplay devices, EL display devices, television devices (TV sets andflat-panel TV sets), cellular phones, and the like.

Forgery can be prevented by providing the semiconductor device 2180 forthe bills, the coins, the securities, the certificates, the bearerbonds, or the like. Further, the efficiency of an inspection system, asystem used in a rental shop, or the like can be improved by providingthe semiconductor device 2180 for the packing containers, the books, therecording media, the personal belongings, the food, the commodities, theelectronic devices, or the like. Forgery or theft can be prevented byproviding the semiconductor device 2180 for the vehicles, the healthproducts, the medicine, or the like; and in the case of the medicine,medicine can be prevented from being taken mistakenly. The semiconductordevice 2180 can be provided by being attached to the surface or beingembedded in the object. For example, in the case of a book, thesemiconductor device 2180 may be embedded in the paper; and in the caseof a package made of an organic resin, the semiconductor device 2180 maybe embedded in the organic resin.

As described above, the efficiency of an inspection system, a systemused for a rental product, or the like can be improved by providing thesemiconductor device 2180 for the packing containers, the recordingmedia, the personal belonging, the food, the clothing, the commodities,the electronic devices, or the like. Further, by providing thesemiconductor device 2180 for the vehicles or the like, forgery or theftthereof can be prevented. Further, by implanting the semiconductordevice 2180 in a creature such as an animal, an individual creature canbe easily identified. For example, by implanting/attaching thesemiconductor device with a sensor into a creature such as livestock,its health condition such as body temperature as well as its birth year,sex, breed, or the like can be easily managed.

Note that this embodiment mode can be freely combined with the precedingembodiment modes.

This application is based on Japanese Patent Application serial no.2007-155620 filed with Japan Patent Office on Jun. 12 in 2007, theentire contents of which are hereby incorporated by reference.

1. A manufacturing method of a semiconductor device comprising the stepsof: forming an island-shaped semiconductor layer over a substrate havingan insulating surface; forming a first insulating film on a surface ofthe island-shaped semiconductor layer by performing a first alterationtreatment; removing the first insulating film; forming a secondinsulating film on a surface of the island-shaped semiconductor layer byperforming a second alteration treatment on the island-shapedsemiconductor layer from which the first insulating film is removed;forming a conductive layer over the second insulating film, wherein anupper end portion of the island-shaped semiconductor layer has curvatureby the first alteration treatment and the second alteration treatment.2. A manufacturing method of a semiconductor device comprising the stepsof: forming an island-shaped semiconductor layer over a substrate havingan insulating surface; forming a first insulating film on a surface ofthe island-shaped semiconductor layer by performing a first alterationtreatment; removing the first insulating film; forming a secondinsulating film on a surface of the island-shaped semiconductor layer byperforming a second alteration treatment on the island-shapedsemiconductor layer from which the first insulating film is removed; andforming a conductive layer over the second insulating film, wherein anupper end portion and a lower end portion of the island-shapedsemiconductor layer have curvature by the first alteration treatment andthe second alteration treatment.
 3. The manufacturing method of asemiconductor device according to claim 1, wherein the first alterationtreatment is a plasma treatment.
 4. The manufacturing method of asemiconductor device according to claim 1, wherein the second alterationtreatment is a plasma treatment.
 5. The manufacturing method of asemiconductor device according to claim 1, wherein the island-shapedsemiconductor layer to which the second alteration treatment isperformed has a film thickness of 10 nm to 30 nm inclusive.
 6. Themanufacturing method of a semiconductor device according to claim 1,wherein the second insulating film has a film thickness of 1 nm to 10 nminclusive.
 7. The manufacturing method of a semiconductor deviceaccording to claim 2, wherein the first alteration treatment is a plasmatreatment.
 8. The manufacturing method of a semiconductor deviceaccording to claim 2, wherein the second alteration treatment is aplasma treatment.
 9. The manufacturing method of a semiconductor deviceaccording to claim 2, wherein the island-shaped semiconductor layer towhich the second alteration treatment is performed has a film thicknessof 10 nm to 30 nm inclusive.
 10. The manufacturing method of asemiconductor device according to claim claim 2, wherein the secondinsulating film has a film thickness of 1 nm to 10 nm inclusive.
 11. Amanufacturing method of a semiconductor device comprising the steps of:forming an island-shaped semiconductor layer over a substrate having aninsulating surface; forming a first insulating film on a surface of theisland-shaped semiconductor layer by performing a first alterationtreatment; removing the first insulating film; forming a secondinsulating film on a surface of the island-shaped semiconductor layer byperforming a second alteration treatment on the island-shapedsemiconductor layer from which the first insulating film is removed;removing the second insulating film; forming a third insulating film ona surface of the island-shaped semiconductor layer by performing a thirdalteration treatment on the island-shaped semiconductor layer from whichthe second insulating film is removed; and forming a conductive layerover the third insulating film, wherein an upper end portion and a lowerend portion of the island-shaped semiconductor layer have curvature bythe first alteration treatment, the second alteration treatment, and thethird alteration treatment.
 12. The manufacturing method of asemiconductor device according to claim 11, wherein the third alterationtreatment is a plasma treatment.
 13. The manufacturing method of asemiconductor device according to claim 11, wherein the island-shapedsemiconductor layer to which the third alteration treatment is performedhas a film thickness of 10 nm to 30 nm inclusive.
 14. The manufacturingmethod of a semiconductor device according to claim 11, wherein thethird insulating film has a film thickness of 1 nm to 10 nm.
 15. Asemiconductor device comprising: a substrate having an insulatingsurface, an island-shaped semiconductor layer provided over thesubstrate; an insulating film formed so as to cover the island-shapedsemiconductor layer; and a conductive layer provided over theisland-shaped semiconductor layer with the insulating film interposedtherebetween, wherein an upper end portion of a cross-section of theisland-shaped semiconductor layer has curvature, and wherein theisland-shaped semiconductor layer has a film thickness of 10 nm to 30 nminclusive.
 16. A semiconductor device comprising: a substrate having aninsulating surface; an island-shaped semiconductor layer provided overthe substrate; an insulating film formed so as to cover theisland-shaped semiconductor layer; and a conductive layer provided overthe island-shaped semiconductor layer with the insulating filminterposed therebetween, wherein an upper end portion and a lower endportion of a cross-section of the island-shaped semiconductor layer havecurvature, and wherein the island-shaped semiconductor layer has a filmthickness of 10 nm to 30 nm inclusive.
 17. The semiconductor deviceaccording to claim 15, wherein the insulating film has a film thicknessof 1 nm to 10 nm inclusive.
 18. The semiconductor device according toclaim 15, wherein when a film thickness of the island-shapedsemiconductor layer is t (t>0) and a curvature radius of an end portionof a cross-section of the island-shaped semiconductor layer is r (r>0),a relationship of t and r satisfies a conditional equation (t/2)≦r≦2t.19. The semiconductor device according to claim 15, wherein when a filmthickness of the island-shaped semiconductor layer is t (t>0) and acurvature radius of an end portion of a cross-section of theisland-shaped semiconductor layer is r (r>0), a relationship of t and rsatisfies a conditional equation (t/4)≦r≦t.
 20. The semiconductor deviceaccording to claim 15, wherein the insulating film includes a materialof the island-shaped semiconductor layer.
 21. The semiconductor deviceaccording to claim 16, wherein the insulating film has a film thicknessof 1 nm to 10 nm inclusive.
 22. The semiconductor device according toclaim 16, wherein when a film thickness of the island-shapedsemiconductor layer is t (t>0) and a curvature radius of an end portionof a cross-section of the island-shaped semiconductor layer is r (r>0),a relationship of t and r satisfies a conditional equation (t/2)≦r≦2t.23. The semiconductor device according to claim 16, wherein when a filmthickness of the island-shaped semiconductor layer is t (t>0) and acurvature radius of an end portion of a cross-section of theisland-shaped semiconductor layer is r (r>0), a relationship of t and rsatisfies a conditional equation (t/4)≦r≦t.
 24. The semiconductor deviceaccording to claim 16, wherein the insulating film includes a materialof the island-shaped semiconductor layer.